[framework] Update StressTestStage to account for read-only transactions

  * New property writeTxPercentage that configures "The frequency of
    transactions that may perform writes (percentage)".
[framework] Create Init- and Continue- StressTestStage to synchronize timers
[framework] Create Init- and Continue- StressTestWarmupStage to synchronize timers
[my-stuff] Split tests using Init- and Continue-StressTestStage
[my-stuff] Split tests using Init- and Continue-StressTestWarmupStage
[my-stuff] Add missing benchmarks :-/
[tdmock] Add sleep times to the ops